It was known in the field of injection molding to provide devices to reduce the time in which to inject molten plastic material into a mold. In U.S. Pat. Re. No. 28,721, granted to Farrell, there is disclosed a device which packs the mold under pressure while allowing the reciprocating screw plasticizer to recover for the next cycle, thereby reducing the cycle time. A similar device is disclosed in U.S. Pat. No. 4,290,701 granted Sept. 22, 1981 to Schad.
A further attempt to reduce the injection cycle time is disclosed in U.S. Pat. No. 4,070,142, granted Jan. 24, 1928 to Farrell, where alternative plasticizers are used in combination with a plastic pump.
In U.S. Pat. No. 4,749,536, granted to Farrell, there is an improvement on the device of U.S. Pat. Re. No. 28,721, namely wherein one cylinder and piston arrangement performs the mold filling operation, while another cylinder and piston arrangement performs mold packing and suck back operations.
While the aforesaid devices were suitable for low capacity injection and injection blow molding operations, the art desired reduced cycle time for high capacity thermoplastic injection. There has recently been a surfeit of waste thermoplastic material for possible recycle. There has also been an industry desire to injection mold large items, such as chairs, building blocks, and the like. The art desired to use this low cost, large volume of waste plastic material to mold large items or products.
It would, however, be economically unfeasible to scale up existing injection molding apparatus, such as a reciprocating screw plasticizer, to meet the present day reduced cycle time and high capacity demands for injection molding.
Now there is provided by the present invention an apparatus for injection molding a high capacity of thermoplastic material in a rapid manner with relatively low cost apparatus.